Fraudsters may use pop-up windows, the small windows or ads that appear suddenly over or under the window you are currently viewing, to obtain personal information. These windows may be generated by "Adware" or "Spyware" programs possibly hidden in free downloads such as screen savers or music-sharing software and installed on your computer. While many of these programs enable harmless advertisements, some contain potentially harmful Trojan horse programs or may monitor your web viewing activity.